Problem: What is the volume of a cylinder with base radius $4$ and height $5$ ? 4 5
The area of the base is simply the area of a circle: $\pi r^2 = \pi \cdot 4^2 = 16 \pi$ The volume of the cylinder is the area of the base times the height: $B \cdot h = 16\pi \cdot 5 = 80\pi$.